EP0943102B1 - Erkennungssystem zur bestimmung der position und anderer objektbezogener information - Google Patents

Erkennungssystem zur bestimmung der position und anderer objektbezogener information Download PDF

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Publication number
EP0943102B1
EP0943102B1 EP97947785A EP97947785A EP0943102B1 EP 0943102 B1 EP0943102 B1 EP 0943102B1 EP 97947785 A EP97947785 A EP 97947785A EP 97947785 A EP97947785 A EP 97947785A EP 0943102 B1 EP0943102 B1 EP 0943102B1
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EP
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Prior art keywords
transponder
transmitter
address
transponders
receivers
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English (en)
French (fr)
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EP0943102A1 (de
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Alan Henry Jones
Andrew Martin Robert Ward
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AT&T Laboratories Cambridge Ltd
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AT&T Laboratories Cambridge Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S11/00—Systems for determining distance or velocity not using reflection or reradiation
    • G01S11/16—Systems for determining distance or velocity not using reflection or reradiation using difference in transit time between electrical and acoustic signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/87—Combinations of sonar systems
    • G01S15/876—Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
    • G01S5/186—Determination of attitude
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
    • G01S5/30—Determining absolute distances from a plurality of spaced points of known location
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/87—Combinations of radar systems, e.g. primary radar and secondary radar
    • G01S13/878—Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/87—Combinations of sonar systems
    • G01S15/872—Combination of several systems for attitude determination

Definitions

  • This invention relates to a detection system for determining information concerning the location of objects, and which can be extended to determine movement and orientation and even physical parameters such as shape of objects in a specified environment.
  • the invention can be applied to people and animals as well as inanimate objects such as furniture, machines, vehicles, equipment and the like, and in this connection object is intended to include any movable entity.
  • Location systems are known which allow the presence or absence of an object in a specified environment (such as a room) to be confirmed or denied, and relative to one or more reference points to identify where in the environment the object is located.
  • EP 0485879 describes a system for locating vehicles in automatic guidance transport systems. Ultrasound is employed as a distance measuring medium whilst an infra-red link allows communication between vehicles.
  • WO95/14241 describes a tracking system which enables a spotlight to follow a person on a stage carrying a transponder. Again infra-red signals are used to instigate ultrasonic transmissions to determine the position of the transponder and therefore the person. The spotlight is moved accordingly.
  • EP 0591899 describes another spotlight controlling system for tracking a moving target (actor on a stage) carrying a transponder.
  • radio transmissions establish the communication link and ultrasound transmissions are employed to determine distance and position.
  • a system which enables the position of each of a plurality of labelled objects in a specified environment to be determined by determining the transit time of slowly propagating energy transmitted from a transmitter on each labelled object to a plurality of receivers positioned at fixed points in or around the specified environment, and computing therefrom the actual distance of the transmitter from the receivers, wherein the transmission of the slowly propagating energy is initiated by a burst of high speed propagating energy form a master transmitter located so as to cause transmitted burst of such high speed energy to enter the said environment, the transmitter on the object being controlled by a receiver adapted to respond to an appropriately encoded burst of such high speed energy, each said burst being encoded so as only to be responded to by one of the object mounted receivers (each transmitter/receiver combination being referred to as a transponder), to thereby initiate a burst of slowly propagating energy therefrom, wherein the burst originating transponder location is identifiable from the encoding of the transmission which triggers
  • the slow speed signals are acoustic or ultrasonic signals and the high speed signals are electric currents or voltage or visible or invisible electromagnetic radiation such as IR, UV or radio signals.
  • Encoding of the high speed signals may be by way of frequency or amplitude or phase modulation or pulse coding or any combination thereof.
  • Such systems are based on the principle of location by multilateration. For each object that is to be located, the straight-line distances are measured from a point on that object to a number of other points in the environment whose positions (in some frame of reference) are already known. Given enough distances, and a suitable geometry of the endpoints between which they are measured, it is possible to derive a position for the object.
  • transmitters and receivers are placed on them and measurements are made of the times of signal pulses being generated and received.
  • a radio pulse for example, can be treated as if its travel time is zero (i.e. independent of range), and it can thus simply be used as a trigger signal.
  • the flight times of the slow signal pulses e.g. ultrasonic pulses
  • the flight times of the slow signal pulses can be accurately measured by synchronising the transmitter and receiver units, as by a timing pulse generated by a suitable controller.
  • Reflections from other objects in the transmitter's environment may cause multiple signals to arrive at a receiver. Any direct-path signal from the transmitter to the receiver should arrive before these reflections, so that in general all pulses arriving at a receiver after the first one should be ignored. For this reason, it is important that the width of the pulse sent by the transmitter is as short as possible, so that the direct-path and reflected signals may be identified optimally.
  • the system is programmed to attempt to derive a position of the transponder.
  • receivers will have detected no signal from the transponder transmitter, due to obstructions, directionality of the transmitting element, etc. These receivers must be excluded from further consideration.
  • the first pulse detected by a receiver is a reflected or diffracted signal. (This may occur, for example, if the direct signal path is obstructed). In this case, the computed distance will be greater than the true distance, and errors would be introduced into the position for the transmitter that is reported by the system if that incorrect distance is used in the position calculation. In general the computed distances would not identify a unique point (or more generally small volume). If this occurs the erroneous computed value has to be identified and eliminated.
  • Reflected and diffracted signals that arrive at receivers can sometimes be distinguished from direct path signals by inspection of the received pulse shape, and thereby inaccurate measurement eliminated.
  • One way of doing this is to compare the distances reported by all pairs of receivers that have detected a slow speed signal. It can be shown geometrically that the difference of the measured distances from two receivers to a transponder transmitter cannot be greater than the straight-line distance between the two receivers, if the measured distances are accurate. Thus, if a pair of receivers is found for which the measured distances to the transponder transmitter do not satisfy this criterion, the receiver that has reported the longer distance can be excluded from further consideration, since reflections and refractions in general will tend to produce longer distance values than the true straight-line distance.
  • the system may be adapted to attempt to fit a non-linear regression model to the remaining distances, by performing an iterative regression computation on the data.
  • the system may be programmed to report that it is unable to calculate the position of the transmitter using the available data.
  • studentised residuals are preferably calculated for the distances, and the system preferably determines the variance of the distance data.
  • Reflected signals will tend to produce large value, so that if the variance is below a predefined, acceptable level, the system can be programmed to conclude that all erroneous signals have been identified and eliminated.
  • signals derived from the receiver associated with the distance that has the largest positive studentised residual is assumed to have resulted from at least one reflection and these signals are first excluded from consideration.
  • the system is programmed to attempt to fit the model again.
  • This procedure involving the deletion of receivers and signals from consideration is repeated as necessary, until the variance of distance data from the remaining detectors is sufficiently small.
  • the geometry or number, or both of the remaining receivers under consideration is insufficient for a three-dimensional position for the transponder transmitter to be calculated. For example, all the remaining receivers may be in line.
  • the system is adapted to abort the computation and report that insufficient information has been gathered to fix the position of the transmitter at that time.
  • the system may use this information for various purposes, or it may transmit the information to other interested parties.
  • the system Before transmitting a second slow speed signal the system preferably waits for reverberations of the previous distance-measuring pulse to die out before attempting to repeat the above procedures to get another fix for the transponder transmitter position. Obviously, the time the system must wait for this to happen will depend on the characteristics of the transmission medium and the transmitter's environment. This may be determined empirically, or by adaptation such as by self-learning.
  • One embodiment of the present invention includes at least three fixed, non-collinearly distributed slow speed signal responsive receivers, at least one transponder transmitter unit for transmitting slow speed signal pulses, mounted on the object, means for generating and transmitting high speed signal pulses to synchronise signal pulse transmission from the transponder with the commencement of a reception-sensitive period at a receiver and means for computing signal pulse reception times and correlating differences therein to determine the required information about the position of the object.
  • a separate transmitter is located on each of two or more objects in the specified environment and each transmitter includes a high speed signal responsive receiver adapted to respond to only one of a plurality of high speed signals, and the separate transmitters are triggered in sequence by a transmitter of high speed signals which is adapted to transmit uniquely one of the plurality of possible high speed signal at the beginning of each timeframe.
  • the invention can be adapted to identify and log movements of two or more objects in the same area/space, by mounting a transponder transmitter on each object and providing each transponder with a unique address, so that each transmitter can be triggered in turn and the position of the relevant object determined in a sequence.
  • transponder transmitters It is not only necessary to trigger transponder transmitters uniquely, but also necessary to restrict transmissions from multiple objects so that they do not interfere with each other, by making sure that the transmissions do not overlap in time in the same space.
  • the coordinating control system which includes means to address the object mounted transponders, and sends address information to them as part of a regular timing synchronisation signal.
  • the slow speed signal transponder transmitters each with their own high speed signal transponder receiver and unique address, could be placed on the objects to be located, and access to the space in which the distance-measuring pulses are transmitted is divided into discrete timeslots, the duration of each timeslot being the time needed for reverberations of pulses to die down.
  • the coordinating device is adapted to send out a high speed timing-synchronisation signal (typically a radio signal) which consists of an address and a timing pulse. All the transponders on the objects will receive this signal, and each compares the received address with its own. If the addresses are the same, that transponder one transmits a slow-transmission-speed distance measuring pulse, when the timing pulse is received.
  • a high speed timing-synchronisation signal typically a radio signal
  • the frequency at which addresses are transmitted by the coordinating device may be varied, either during set-up, or based on information obtained from previous addressings.
  • an object which will normally be static and remain for long periods of time in one place can be identified as such, and its address only transmitted infrequently - say once every 5 minutes or once every hour.
  • objects which it is known in advance are likely to move (or be moved) within the space, can be identified as mobile, and their transponder addresses transmitted more frequently - eg once every minute, or every few seconds, or even more often if the system capabilities permit.
  • a memory in the coordinating device may be used to store against each address, an item of information which indicates the frequency of position changes, for that address, detected by the system during some predetermined period of time (which might be minutes, hours or days depending on the environment and the nature of the objects carrying the transponders).
  • the stored item of information is employed to determine how often each address is broadcast. If the item of information changes in value, indicating an increased or decreased frequency of movements of the address within the space, the coordinating device can respond appropriately and increase or decrease the frequency of transmissions of the address received.
  • the system can also be used to determine the true orientation of an object, by comparing the position of two or more transponder transmitters mounted on the object.
  • the positions of all the transponders can be found in three dimensions. Since the fixed spatial relationship between the transponders on the object is known, as well as their measured positions in three dimensions, it is also possible to determine the orientation of the object.
  • one or more transponder transmitters located thereon will enable the position and orientation of the object to be determined.
  • an object mounted for rotation about a fixed axis and only capable of that movement will generally only need one off-axis transponder to be mounted thereon to allow its rotational position to be computed.
  • the same pattern of addressing is preferably maintained so that changes (caused by movement) in the actual and/or relative positions of the transponders will be as small as possible, and the most accurate description of each orientation as well as the movement of the object will be obtained.
  • the coordinating control system memory means typically stores a unique address for each of the transponders, and the control system is programmed to encode the transmissions using the address information so as only to address the transponder transmitters individually.
  • At least one additional item of information is stored in a manner which can be associated with each unique address, and the control system is programmed to select from the addresses that of the receiver/transmitter combination next to be polled, using the WHISP values to determine the order of addressing.
  • WHISP weighted hierarchy indication for schedule positioning
  • the coordinating control system may be separate from or form an integral part of the master transmitter.
  • a WHISP may be stored for each unique address, and it is the WHISP which must be changed to adjust the subsequent addressing of the transponders.
  • WHISPS a set of standard WHISPS may be stored and an association between each unique address and one of the standard WHISPS is stored for each unique address, so that an appropriate WHISP is linked to each unique address. In that event only the associations need to be changed so as to influence the subsequent addressing of the transponders. Likewise a change to one (standard) WHISP will mean that all the associated addresses will be given a new hierarchial position.
  • WHISPS For complete flexibility unique addresses, WHISPS, (and/or the associations between unique addresses and WHISPS) can all be changed to allow for the entry or exit of transponders into and out of the environment, and to alter the manner in which those in the environment will be addressed by the coordinating control system.
  • the WHISP may be a simple logic 1 or 0 to indicate whether the transponder combination is to be addressed or not.
  • the WHISP may comprise a priority or weighting measure to determine the order or rate at which the transponder is to be addressed.
  • the WHISP may comprise two items of information, firstly for example the length of time since the transponder was last addressed (which may be continually updated by clock information) and secondly for example a rate of interrogation figure to be achieved by the system for that transponder.
  • the coordinating control system may compile a list of transponders to be addressed in a sequence by interrogating all of the unique addresses and their related WHISPS and compiling the order in which they are to be interrogated using the current WHISP information.
  • the coordinating control system may create a schedule of unique transponder addresses using the WHISP data, and arrange the order of the addresses in the schedule, and therefore the order in which they are to be interrogated.
  • the schedule is then used to determine the encoding of each trigger burst from the master transmitter and the order in which the transponders are thereby interrogated.
  • any changes which are required to be made to WHISP data may be held over pending the end of the interrogation of the current schedule of addresses, whereupon the WHISP data is updated prior to the compilation of the next schedule.
  • a change to a WHISP may be permitted to interrupt the running of a particular schedule if the unique address or addresses associated with that WHISP is/are still to be interrogated, but is held over to update the WHISP data before the next schedule is compiled if the particular address or addresses has/have already been interrogated in the current schedule.
  • the system may include an emergency override to allow the transponder triggering in accordance with the current schedule to be terminated immediately, and for a new schedule to be immediately compiled, taking account of the WHISP change associated with, or entered with or after, the emergency override instruction.
  • Changes to WHISP data may occur as a result of a lapse of time, the arrival of a particular time or date, or by interaction with an application running on a computer (which may be part of the position determining system, or the coordinating control system, or another computer altogether), or by the entry of data by an operator for example to indicate that the system should cease its scheduled transponder position determining function and for example seek one particular transponder (which may for example relate to that on a particular person or object believed to be within the environment).
  • environment related information may be allowed to create an interruption to permit or cause WHISP data to be altered, such as an increase or decrease in temperature, light level, or sound level or the like, either within the environment or within a separately monitored environment, or by transducer originating signals linked for example to the movement of an object either within the environment; within an adjoining environment; or for example by the opening of a door communicating between one environment and another.
  • the movement of an object within the monitored environment or an adjoining environment may be detected by means of a movement sensor such as a trembler switch, associated with the object. If so a radio or hard-wired communication channel may be required between the sensor and the coordinating control system.
  • a movement sensor such as a trembler switch
  • references to changes to WHISP data include changing the WHISP data stored in a unique memory means linked to one of the unique addresses, or changing the association between a transponder address and a plurality of standard WHISPS, depending on whether a separate WHISP is stored for each address, or whether a number of standard WHISPS are stored and associations between them and the different transmitter addresses are stored.
  • the scheduler may be adapted not only to determine the order in which the transponders are to be interrogated but also the rate of interrogation of any one transponder.
  • This may for example be a fixed rate associated with the particular transponder address, which rate is entered as a second item of information in each WHISP.
  • the second item of information may be an adjustable rate value, which can be altered in relation to variations in a parameter monitored by a transducer or sensor.
  • the parameter may for example be temperature, light level, sound level or the like, or may be a value which can be adjusted by an operator, or in relation for example to a parameter such as the time, or the date.
  • the rate parameter associated with each WHISP itself may be a dynamic variable, whose instantaneous value is determined for example by whether a variation has occurred in the detected position of a transponder carried by an object.
  • the position(s) of the transponder(s) carried by the object(s) will be substantially identical each time the system interrogates the relevant transponder(s).
  • the system can be programmed so as to reduce the frequency at which any one transponder (or group of transponders) is interrogated, down to a relatively low level, thereby reducing the traffic on the system and allowing more time to be available for more frequent interrogation of transponders positioned on objects which are moving, and whose positions therefore are likely to vary from one reading to the next.
  • the system may be programmed to utilise a third item of data within a WHISP, and to increase the tracking, (ie frequency of interrogation) of a transponder of a first object if a second object having such a third item of information stored as part of its WHISP is perceived by the position determination of the transponder on the second object, to have moved close to the first object.
  • the WHISP of a transponder address of a human being may carry such a third item of information, so that if the transponder linked to the person concerned is seen by the system to approach an object which is normally stationary and whose transponder would otherwise be interrogated perhaps only once every 5 minutes, the interrogation rate of the transponder associated with the stationary object may be increased in anticipation of the possibility that the person may suddenly move it.
  • a fully dynamic system can be created since it allows the scheduler to alter not only which transponder is to be interrogated but also the rate at which different transponders are to be addressed with complete flexibility, thereby to follow changes and developments in an environment, with little or no delay.
  • the system can therefore be thought of as having very low hysteresis and by including pre-programmed items of information in each WHISP, which can alert the system to the likelihood of changes occurring, so sudden changes in the environment can be followed almost immediately they occur.
  • a location system that uses a set of ultrasound receivers placed at known positions on a ceiling in a room to detect ultrasonic signals from an ultrasound transponder transmitter attached to an object in the room.
  • the system can be extended to locate more than one ultrasonic transponder transmitter in the room, provided each has a unique address so that they can be triggered separately, typically by serially polling the transponder transmitters.
  • a central coordinating device triggers the transponder transmitter, at the same time as a reset signal is sent to the ultrasound receivers, typically over a wired network. Synchronisation between the transmitting and receiving elements of the system is thus achieved.
  • each ultrasonic transponder transmitter is controlled by a transponder radio receiver and is triggered by the transmission of a suitable radio signal into the room.
  • Each transponder receiver includes a unique address. The radio signal contains one such unique address.
  • each radio receiver compares the transmitted address with its own, and, if the addresses match, its ultrasonic transponder ransmitter is triggered to emit a short pulse of ultrasound.
  • the central coordinating device has to allow for reverberations and reflections of each transmitted pulse to die away (so that the ultrasound receivers detect ultrasound from only one source) before triggering another ultrasonic transponder transmitter.
  • the time needed to allow all such sounds to die away can be of the order of 20ms.
  • Efficient distribution of the timeslots between ultrasonic transponder transmitters to be located is clearly a priority, and this distribution should take account of the different rates at which location information about particular objects is desired.
  • the system might normally monitor transponders carried by people (who move often) at least once each second, whereas it might monitor those attached to desks, filing cabinets or workstations (which move infrequently) only once a minute. If, however, a monitored person walks up to a particular workstation, the system may be programmed thereafter to monitor that workstation's position once a second at least while the person is noted as being in the vicinity, because it is then more likely to be moved.
  • a further constraint on the allocation of timeslots can arise when members of a group of transponders need to be interrogated in consecutive timeslots. This is advantageous when the positions of the transponders in the group are to be used to determine both the location and orientation of an object, such that any motion of the object between readings can make the derived information inaccurate.
  • Scheduler software, typically in the form of an algorithm for performing this function.
  • the priority level assigned to each different transponder is called its Location Quality of Service (LQoS).
  • LQoS Location Quality of Service
  • the LQoS of a transponder may also be changed at any time, and subsequent timeslot allocation needs to take account of any such changes.
  • the Scheduler provided by the present invention is designed to accommodate LQoS changes; to have the appropriate long term behaviour; to assign timeslots to transponders based on their Location Quality of Service (LQoS); and furthermore to deal with service demands which are greater or less than the system capacity, by scaling excessive requests fairly in the former case, and padding with dummy timeslot assignments in the second. It is also capable of adjusting timeslot assignment to allow a group of transponders to be located consecutively.
  • LQoS Location Quality of Service
  • the Scheduler is adapted to maintain a scheduling table stored in memory.
  • Each row of the table contains six entries:
  • a row in the table is described by an ordered six-type (a,g,l,e,s,b).
  • a global flag called “excess-demand” (to be described later) and an integer called “last-group” are also maintained by the Scheduler.
  • the scheduling table is empty. A single row (0,0,1,1,0, false) is immediately added. This entry represents a dummy transponder. The excess-demand flag is set to false, and the last-group is set to zero.
  • An operator (user) or software application can contact the Scheduler over its CORBA interface to indicate that the location requests for a transponder group should be added or changed. It should be noted that if two or more transponders are members of the same transponder group, then their location requests should not be capable of being added or changed separately. Furthermore, the requests involving the dummy transponder address 0 and dummy transponder group ID 0 will be ignored.
  • the user or application passes the following information to the scheduler:
  • the scheduler For each transponder address a 1 ,....a n , the scheduler then adds or modifies an entry in the scheduling table.
  • the scheduler is then arranged to recalculate the ELQoS for each of the m entries in the table.
  • Equation (2) it updates the ELQoS for each of the n entries in the scheduling table, e i , with a new value e' i . If t is less than 1, then e' i is given by Equation (2).
  • Equation (3) e' i is given by Equation (3).
  • the Scheduler When a user or application contacts the Scheduler over its CORBA interface to indicate that a location request for a transponder should be deleted, it also passes the address of that transponder a i , to the Scheduler. (The entry corresponding to transponder address 0 may not be removed). If the scheduler finds that an entry for that transponder is present in the table, it removes the corresponding row (a r ,g r ,e r ,s r ,b r ) from the table.
  • the scheduler then updates every other row in the table (a x ,g x ,l x ,e x ,s x ,b x ) to (a x ,g x ,l x ,e x ,s' x ,b x ) where the value of S' x is given by Equation (4),
  • n is equal to the number of rows in the table before removal of the location request.
  • the scheduler recalculates the effective rates based on the remaining table entries as described in the previous section.
  • the Scheduler must tell the central coordinating device (across a CORBA interface) the address of the transponder which should be located next. It does this by examining the contents of the scheduling table and any attempts to update the table are blocked until this examination is complete.
  • the Scheduler steps through each row in the scheduling table. If the last-group register does not contain 0, and the scheduler encounters a row in which the transponder group ID is the same as the contents of the last-group register, and in which the swap-slot bit is false, it sends the transponder address contained in that row to the coordinating device, and sets the swap-slot bit on that row to "true".
  • the relative positions of two or more transponders carried by the same object can be checked against their previous known positions to determine whether or not the object has for example been rotated.
  • a set of two or more transponders which are carried by the same object can be identified as such with a further item of information in their associated WHISPS, such that the control system will schedule the interrogation of the second and any subsequent transponder addresses of the set of transponders on the object after the first of the pair has been interrogated.
  • transducers In general three transducers are needed to permit the orientation (and any changes in orientation) of an object to be determined. For some objects normally constrained to occupy a limited range of positions only two or even one transducer may be sufficient.
  • further memory means is provided within which is stored data relating to the time at which each transponder address was last interrogated, and the programme running in the processor controlling the said logic means is adapted to compare the information stored in each said further memory means with the WHISP data for all transponder addresses suspected to be in the environment, to determine which of the transponders is next to be interrogated, and to encode the next radio trigger signal accordingly.
  • the different memory means may comprise different parts of one memory device (such as a large random access memory) or may be formed from two or more different memory devices, at least some of which may be random access memories and others may be programmable read only memories.
  • any acoustic noise sources in the environment which can generate ultrasonic signals similar to those sent by the ultrasound transponder transmitters, have the potential to introduce false position determination.
  • the ultrasonic receiver is rendered sensitive only to sound of a particular frequency, by the use of an ultrasonic detector with a narrow bandwidth around that frequency, and the bandwidth of the sound signal emitted by the transmitter is also limited to a narrow bandwidth around that frequency
  • the system includes a further ultrasonic receiver adapted to simultaneously monitor sound at at least one of a number of different frequencies, and a logic based system determines if a signal detected by a receiver at the unique frequency used by the transmitter is accompanied by other sounds at some or all of the said different frequencies and if not, the detected signal is identified as being TRUE, and if accompanied by other sounds, the detected signal identified as being corrupted by noise.
  • noise sources in the environment for example, a set of jangling keys
  • noise sources in the environment tend to simultaneously generate signals at a large number of different frequencies, so that sounds are detected at the transponder transmitter frequency and at other frequencies simultaneously.
  • the detection of such a range of sound signals has to be identified as either a FALSE sound signal or is as a TRUE signal which has been corrupted by noise, and in either event the signal must be rejected.
  • the number of additional frequencies that are monitored is preferably greater than one, and the monitoring may be performed at one or more of a number, of different points in the environment.
  • a plurality of transponders may be attached to the same object.
  • three transponders are attached to a rigid object so that they are not colinear, then by finding the positions of those three transponders not only the position but also the orientation of the object may be deduced (assuming that no movement of the object has occurred between the time at which the measurements were made).
  • each transponder typically has its own independent radio interface, controlling logic, and one or more ultrasonic transducers.
  • controlling logic typically controls the operation of each transponder's own independent radio interface, controlling logic, and one or more ultrasonic transducers.
  • ultrasonic transducers typically be placed on an object, complete physical independence of the transmitters is not required and components of different transmitters can be interconnected using wires and duplication of components which are common to the transponders can be reduced or eliminated.
  • a single radio receiver may be provided together with decoding logic to drive a number of individually addressable ultrasonic transducers.
  • the one receiver will respond to more than one address and hence can be described as a Multiple-Address transponder but for each address only one of the ultrasonic transducers would be triggered, corresponding in each case to one of the points on the object.
  • the invention thus envisages an object having mounted thereon a plurality of ultrasonic transducers located at a corresponding plurality of different non-collinear positions on the object, and a single radio receiver adapted to trigger one or another of the transducers depending on an address code contained within a radio signal received thereby, so that the different transducers may be triggered by appropriately coded radio signals, to transmit ultrasound signals into the environment at specific times, and from the different points on the object, to enable the unique positions of the said points on the object to be determined and enable the orientation of the object to be determined.
  • each transducer as being comprised of a group of two or more similar transducers facing in different directions to more uniformly spread the ultrasound around the environment.
  • the basic ultrasonic transponder transmitter incorporates a plurality of ultrasonic transducers which are driven simultaneously to create a pulse of ultrasound from the device.
  • the transducers (which, individually, have a relatively narrow beam angle) are arranged to point in different directions so as to generate a generally omnidirectional transmission pattern.
  • the transducers it is possible to arrange the transducers so as to produce a more directional beam, and two advantages follow:
  • the transponders are made aware of the fixed interval which is to occur between addressing messages and power saving is achieved by turning off the radio interface after a message is received and switching it on just before the next one is due.
  • Further power saving may be achieved if the frequency with which a particular receiver-transmitter will be addressed by the coordinating device is known. If the coordinating device is programmed so as to be aware that the transponder will not be addressed for some amount of time, it can encode that time in the radio message, and after decoding the message the transponder will be able to switch off its radio interface for that amount of time.
  • the power saving is particularly efficient if a transmitter is made to "sleep" for a long time, as would be the case if the transponder is being used to track, an item of office equipment such as a printer, which is not expected to move very often.
  • the scheme described above can be extended to allow sleeping transponders to be woken up at short notice.
  • the transponders can be configured so that they turn on their radio interfaces once a second, at a time when a message is due, and decode that message (therefore using 1/50 of the power which would have been used if they had decoded each message).
  • a data bit at the start of each message indicates that the coordinating device wishes to wake up all sleeping transponders or a set of sleeping transmitters (say, all those with even addresses).
  • the "sleeping" transponder can be grasped and woken up accordingly by transmitting an appropriate code, within the capability of the bits. If a sleeping transponder receives such a message, and if that message is applicable to it, it will wake up, and from that time on check every addressing message from the coordinating device, until such time that it is instructed to go to sleep again. With this method, much of the power-saving advantage of sleeping can be retained, and yet it can quickly trigger a transponder so as to be able to determine its location. Thus in the case of the printer described above, if a person walked up to the printer, it is likely that they might move the printer, and in which event it may need to start tracking it immediately, even if it was currently "sleeping" to save power.
  • a transponder If a transponder is taken out of range of the master radio attached to the coordinating device, there is no point in it continually turning on its radio interface, for it will be unable to receive addressing messages. Therefore, in order to save power in these circumstances, if a transponder does not receive an addressing message at a time when one is expected, then it can be programmed to go into sleep mode for a predetermined period (perhaps one minute), before turning the radio channel on again for sufficient time to detect whether it is in range of the coordinating device again. For example, if the coordinating device was sending out an addressing message every 1/50 second, then a sleeping transmitter must wake for 1/50 second to determine if it is in range of that coordinating device.
  • the radio interface would use only 1/300 of the power it would otherwise use. This is achieved at the expense of up to a one minute delay before a transponder's position can be determined after it is back in range of the coordinating device.
  • a bidirectional radio link is provided between a remote receiver and each transponder. Typically this is achieved by adding a radio transmitter to each transponder and adding a radio receiver to the master transmitter.
  • Such transponders will be referred to as bi-directional transponders.
  • the coordinating device may for example transmit the radio receiver addresses in sequence of all possible bi-directional transponders, at regular intervals.
  • the bi-directional transponder radio responses may be checked for radio responses from any new transponder addresses, and these addresses may then be added to the list of bi-directional transponder addresses which are to be scheduled, for position determination by subsequently triggering by radio their bi-directional transponder so as to generate ultrasound signals.
  • a "Slotted ALOHA contention-resolution protocol” such as described by Roberts L in ALOHA Packet Systems With and Without Slots and Capture, Computer Communications Review, April 1975, may be used to allow the transponder to identify its unique identification (ID) to the coordinating device and establish its position in the schedule for the master transmitter.
  • ID unique identification
  • This type of protocol is a probabilistic protocol which allows many transmitting and receiving devices to use the same radio channel to transmit at the same time. This allows a plurality of transponders to use the same radio channel to communicate with the coordinators and enter their ID's into the schedule to be used by the master transmitter.
  • the contention-resolution protocol is performed until an indication is received from the master transmitter and/or its associated coordinator that location resources have been allocated to the new ID for that transponder transmitter.
  • This indication may be sent as part of the addressing message.
  • the indication may simply be a command to transmit or a separate acknowledgement field.
  • the transponder's unique radio receiver ID may be encoded in the message to show that the master transmitter and/or coordinator is aware of its presence.
  • registration may also be used in resource retrieval to prevent valuable resources being used unnecessarily.
  • the coordinating device may be programmed to reallocate the location resources that were are being used to track that device.
  • the coordinating device may be programmed to set a "transmit" bit in the radio addressing message the next time it is transmitted by the master transmitter, so as to force a registration from the addressed transponder transmitter, whilst blocking registration attempts from any other bi-directional transponders.
  • the related object mounted transponder is still in range of the master radio transmitter, and the absence of an ultrasound response either lies in a temporary shielding of the transponder or an electrical failure, (as opposed to movement of the object), and the resource should not be reclaimed.
  • the transponder may have been temporarily shadowed by ultrasound absorbing material.
  • the coordinating device may be programmed to set a special drop bit in the addressing message, to indicate that the location resources that are currently allocated to that transponder will be reclaimed, and the transponder concerned will not subsequently be addressed via the master transmitter radio link.
  • the transponder radio receiver If the transponder radio receiver can receive this message, it must be in a location where it can receive radio signals from the master radio transmitter but the coordinator is unaware of its ultrasonic response. In this event the bi-directional transducer is programmed to perform the registration process described above, but in the meantime the coordinating device reclaims the now unused location resource associated with that ID, until such time as the transducer achieves registration.
  • Each addressing message may contain one or more sets of error-correcting or error-detecting bits in combination with a powerful checking algorithm (e.g. CRC Check).
  • CRC Check a powerful checking algorithm
  • a transponder receives a message containing errors, it is programmed to assume that the message was destined for it, and that the drop bit was set, so that if a transponder receives such a message, it will immediately begin the registration process.
  • either the overall device or all of the regional coordinating devices may be programmed to remember the ID's of any bi-directional transponders which have dropped out, and this fact may be compared with a look up table of data, indicating whether or not an alarm is to be raised and/or the absence noted in a display. For example in the case of an ID associated with a valuable piece of apparatus, a burglar alarm may be sounded, and exit down remotely locked.
  • the overall coordinator may likewise be programmed to raise an alarm, bar access or exit, and/or display this in a display.
  • input and output facilities may be provided on the transponders.
  • a radio message from a coordinating device may contain a number of data bits (an "Output Data Value") which may, for example, be sent to an output port on the addressed transponder, to control for example a display, or robotic device associated with that transponder.
  • a set of ultrasonic receiving elements are placed in a matrix on the ceiling of rooms in which the system is installed, and ultrasonic transmitters are placed on the objects to be located.
  • An addressable radio link is used to allocate timeslots, transmit the synchronising timing pulse, and allow transmitting elements to communicate with a coordinating device, eg to register an initial presence.
  • Waves are used because their speed of propagation is very fast, and unknown delays in the radio link will be very small compared to the time-of-flight of, for example, ultrasonic pulses used to measure distances so that to a first approximation the measurements can be said to be synchronised, and the unknown errors will not significantly reduce the accuracy of the system.
  • a wired network may be used between the fixed receiving elements to distribute a timing pulse. This has the advantage of being less prone to interference, and potentially of lower cost.
  • At least three receivers must detect valid signals for the system to be able to calculate the position of the transmitter, but if all the receiving elements are coplanar, there can be ambiguity about whether a transmitter is above or below the plane containing the detector - eg the ceiling of a room. This ambiguity can be resolved if it is known for example that all transmitters are always below the ceiling.
  • the information gathered by this system can be used to automate computing and communications equipment in an intelligent manner.
  • Availability of fine-grain high resolution location information can allow new methods of human-computer interaction, e.g. connection of video and audio streams by bringing their endpoints into close physical proximity.
  • a transmitting unit as an input device, e.g. as a wireless mouse, a 3D pointer, or for three-dimensional gesture generation.
  • Power is typically derived from two 3.6V half-AA lithium thionyl chloride batteries, regulated to 5V by an LT1129 IC.
  • a number of these are located at known locations around the environment (room) in the ultrasonic positioning system.
  • each receiver 47 is triggered by a central controller 48 across a network 50.
  • the receiver monitors signals from a 40KHz ultrasonic detector 52 for 20ms as depicted in Figure 6(B), and the time at which the incoming signal peaked for the first time is determined and held in the receiver.
  • the central controller 48 polls each receiver across the network 50 as depicted at 54 and 56 in Figure 6(C), and retrieves the time value. The value from each receiver is either the time after the window opened at which the signal first peaked, or is zero (which indicates that no useful signal was detected).
  • the first detector 52, and first channel 58 are sensitive to 40 kHz and the second, 60, 62 to another frequency eg 25kHz.
  • both channels are reset and monitor the incoming signals for 20ms, and determine the times (a,b) at which any received signals peak for the first time as shown in Figure 7(B).
  • the value b is checked and if greater than O, the value of a is forced to O, also, as shown in Figure 7(C). If b equals O, the value of a is available to be returned to the central controller.
  • a standard receiver-transmitter (transponder) unit 68 (such as item 10 in Figure 1) is shown in Figure 8.
  • This comprises a radio receiver (1) which picks up encoded FM signals in the 418MHz band from a radio transmitter (16 in Figure 1) controlled by a central coordinating device 48 (not shown).
  • decoding logic 72 which presents the address contained in any decoded message, to an address comparator 74. If the latter identifies the address in the message as that of the transponder stored in ROM 76, it triggers a signal generator 78, which drives a set of ultrasonic transducers 80 to transmit an ultrasonic pulse.
  • Two such standard transponders 82, 84 are shown in Figure 9 attached to two spaced apart points on a chair 86.
  • a single receiver and control unit 88 drives two individually addressable ultrasonic transducer sets, mounted at the same points on the chair 86, 90, 92 as were the standard transponders 82, 84.
  • the unit 88 is made up of a radio receiver 94 which picks up the encoded FM signals in the 418MHz band from the central transmitter. These signals are passed through decoding logic 96, which presents the address contained in any message detected to an address comparator 98.
  • the latter is associated with a lock-up table 100 containing in this case two rows 102, 104. Each row stores a transducer address and a port number (e.g. If transducer set 1 is attached to port 1, one of the rows will be the ordered pair (1,1)).
  • the address comparator identifies that the address in a received radio message matches one of the transducer addresses in the look-up table 100 it triggers a signal generator 106.
  • the address comparator also controls gates 108, 100, to direct the output of the signal generator 106 to the port identified by the port number in the received transducer address. It can be seen therefore that the number of radio receivers, decoders, comparators and signal generators required by a system where two or more ultrasonic transmitter transducers are to be mounted as single objects, can be reduced, with consequent economies.
  • Two groups of ultrasonic transducers 112, 114 are connected separately one to port 1 (controlled by gate 108) and the other to port 2 controlled by gate 110.
  • FIGS 12A and 12B A less directional transducer is shown in Figures 12A and 12B. This comprises a spherical body 116 from which protrude a plurality of regularly spaced transducers, one of which is shown at 118 in each of the views.
  • the device 120 is shown mounted on a housing 124 which may contain electronic components making up the transponder. Less than half the number of transducers are required than in an omnidirectional source such as shown in Figures 12A, 12B.
  • FIG 14A shows a transponder 126 capable of being worn by a person around their neck for example on a chain 128.
  • the ultrasonic transducers 130 can be arranged to give a relatively narrow beam 132 which will project in front of the person 134.
  • transponders omnidirectional standard
  • the objects on which transponders omnidirectional (standard) are attached are opaque or relatively opaque to ultrasound
  • a transponder 136 attached to a known point 138 on such an object 140 as in Figure 15.
  • the opacity of the object 140 ensures that the only sound energy 142 which can leave its vicinity does so in the direction 144. This effect may be amplified if the transmitter is itself directional to some degree.
  • the location system can calculate in three dimensions the position (x,y,z) of the transponder 136.
  • the location system also knows the positions (u 1 ,v 1 ,w 1 ) ... (u n ,v n ,w n ) of the n receivers that have detected the ultrasonic signal.
  • the direction, relative to the object, in which the ultrasonic energy will have left its vicinity can be deduced. Correlating these three items of information allows the object's orientation to be determined, where the position of point 138 relative to the object 140 is known.
  • the person 146 is wearing a transponder 152 on a chain around his neck.
  • the sound energy is directed in front of the person, with the middle of the beam lying in the same vertical plane as the direction in which they are facing.
  • Figure 18 shows the person from above and the area in the horizontal plane over which sound energy will be radiated from the ultrasonic transducers on the transponder 152.
  • the vector (a,b,c) is computed from the transponder to the mean point.
  • the vector a, b, c is computed using Equations 18, (9) and (10).
  • the vector (a,b,0) usually can be taken to be a good estimate of the horizontal direction of the middle of the sound beam leaving the object's vicinity, and can be used to calculate the direction A, in which the person is orientated around a vertical axis (relative to some other horizontal direction specified by a vector (m, n, 0).
  • a in the range [- ⁇ , ⁇ ] can be computed from the values of sinA and cosA given by Equations (11) and (12).
  • the value of A can be used as an estimate of the direction in which the person is facing.
  • FIGS. 18 to 23 illustrate a position detection system embodying the invention and the separate parts making up the system.
  • FIG 18 is a block schematic diagram of the complete system in which a Scheduling PC 154 dictates which one of a set of Mobile Transponders (one of which is shown at 156) are to be addressed in each of 25 timeslots per second. Addressing messages generated by the Scheduling PC are sent to Mobile Transponders via a Zone Manager 158, which also passes registration messages from the Mobile Transponders 156 back to the Scheduling PC.
  • a Scheduling PC 154 dictates which one of a set of Mobile Transponders (one of which is shown at 156) are to be addressed in each of 25 timeslots per second.
  • Addressing messages generated by the Scheduling PC are sent to Mobile Transponders via a Zone Manager 158, which also passes registration messages from the Mobile Transponders 156 back to the Scheduling PC.
  • Ultrasonic signals generated by the addressed Mobile Transponders 156 in response to the addressing messages sent by the Zone Manager are detected by a set of Receivers three of which are shown at 160, 162, 164 attached to a Matrix Manager 166.
  • a Matrix Manager typically, there will be one Matrix Manager and a set of Receivers per room (or other space in which ultrasound is confined).
  • a Positioning PC 168 connected to the Matrix Manager 166 derives the air temperature of the room in which the polled receivers are located via a thermometer 170, and polls the Receivers 160, 162 etc to retrieve the three measurements derived from the received ultrasonic signals, and uses this data, and the measurement of air temperature in the room 172, to calculate the 3D position of the source of the ultrasonic signals.
  • a second set of receivers (174, 176, 178) in a second rom 180 are also shown, with associated matrix manager 182 and positioning PC 184.
  • Other similar set-ups can be provided for each room in a building, each linked to a central area manager 186.
  • Radio signals are transmitted to the mobile transponder radio receivers from a master radio transmitter/receiver unit 189 operating at 418 MHz with FM encoding.
  • the Clock Generator 188 sends an accurate 25Hz clock pulse and global time value to the Zone Manager and the Matrix Managers across a serial network.
  • the generator has a 25Hz 192 clock which drives a time store and counter 194.
  • the time store holds the current global time value, and the counter increments it with every pulse.
  • An initial global time value may be loaded from a the PC 190 connected to the Clock Generator (see Figure 18).
  • serial network interface 196 After incrementing the current global time value, that value, and the clock pulse are gated to a serial network interface 196, which distributes these signals to other system components, so as to synchronise them.
  • Each Zone Manager (158, 166, 182 etc in Figure 18) handles the radio interface between the Scheduling PC and the Mobile Transmitters. As shown in Figure 20, it has a Data Store 198 which is filled by the Scheduling PC with the next packet to be transmitted. When this process is complete, the Zone Manager unasserts the "Ready" status line. On receipt of a clock pulse from the synchronisation network (200) along 202, the Zone Manager stores the associated time in a Time Store, 204, and triggers a Message Generator 206.
  • the Message Generator sends a 136-bit preamble followed by a Manchester-encoded copy of the stored packet at 40kbps co the transmit side of a 418MHz FM Radio Transceiver 208, thus sending a DC-balanced copy of the desired message to the Mobile Transmitters.
  • the Zone Manager After sending the message, the Zone Manager triggers a Message Decoder 210, which looks at the incoming signals picked up by the receive side of the Transceiver 208. Any incoming radio message sent by the radio transmitting section of the Mobile Transponder is decoded and error-checked, and if the message is valid it is stored in a Message Store 212.
  • the Zone Manager When time has been allowed for the outgoing message to be sent and any incoming messages to be detected, the Zone Manager asserts the "Ready" status line, indicating that the Scheduling PC can review the stored time and any stored message. To this end the scheduling PC controls Data Path Switch 214 to supply trigger tune (from 204) and/or message (from store 212) as appropriate, before loading the next packet to be transmitted.
  • the global clock synchronisation network signals pass unchanged through the Zone Manager.
  • the Scheduling PC 154 ( Figure 18) is programmed to determine the order in which Mobile Transmitters should be addressed based on the Location Qualities of Service (LQoS) assigned to them (either statically, or dynamically by users and applications).
  • the Scheduling PC also constructs the packets to be sent to Mobile Transponders (via the Zone Managers), and performs resource reclamation.
  • LQoS Location Qualities of Service
  • the Scheduling PC determines whether an application requires that an "Output Data Value" should be sent to that transmitter. It also determines whether applications have indicated that the transmitter is no longer responding to addressing messages (perhaps because it has been removed from the range of all the receivers in the room or building in the case of a multi-zone system). If so, the transmit or drop bits in the next message should be set, to check the situation, or reclaim resources (as described above).
  • the Scheduling PC also determines whether any Mobile Transmitters should be woken prematurely frcm a sleeping state, in which case the wake bit should be set. It also can acknowledge chat a mobile transponder has been registered with the system whether this has been done by an operator, or an application according to data/time or data forcing the system to look for a particular mobile transponder addrass or has been achieved automatically.
  • a message packet is then constructed from the collected information.
  • the packet has a number of Cyclic Redundancy Check (CRC) error checking codes embedded within it (the standard CRC-8 code is used), and its format is given in Table (A).
  • CRC Cyclic Redundancy Check
  • the Output Data Value field is set to 255. Similarly if no Mobile Transponder registrations require acknowledgement, the Registration Acknowledgement field is set to zero.
  • the message packet is loaded into the Zone Manager's Data Store in 8-bit chunks. After the last chunk is loaded, the Scheduling PC start to continuously poll the Zone Manager's "Ready" status line. This line is asserted when the Zone Manager has transmitted any stored message where the radio receiver section of the transceiver 208 is being employed.
  • the Scheduling PC retrieves (from the Zone Manager) the time at which the transmission was made, and sends an event of the form (identifier, time) to the Area Manager across a COR3A interface (Object Management Group, The Common Object Request Broker; Architecture and Specification. Revision 1.1, OMG Document Number 91.12.1, December 1991), indicating the 16-bit identifier of the addressed Mobile Transmitter and the time of addressing.
  • a COR3A interface Object Management Group, The Common Object Request Broker; Architecture and Specification. Revision 1.1, OMG Document Number 91.12.1, December 1991
  • the Scheduling PC retrieves from the Zone Manager any incoming message sent by the radio transmitter of the address Mobile Transponder (where fitted and utilised). Any such message will contain an address and button status bits.
  • the Scheduling PC must deal with any registration request detected in this way, and/or inform any applications which are interested in "Button Pressed" events from Mobile Transponders.
  • the Matrix Manager shown in Figure 21 resets ultrasound Receivers (eg 20, 22 etc in Figure 1) connected to it, at a precise time, and acts as an interface between the Positioning PC and those Receivers.
  • the Matrix Manager On receipt of a clock pulse along line 216 from the synchronisation network 200, the Matrix Manager stores the associated time in a Time Store 218, limits for 9.65ms to allow the radio message to be sent and sends a "Reset" signal over its Downstream Network Interface 220 to the ultrasound Receivers connected to it. After 20ms, the Matrix Manager asserts the "Results Ready” status line, which indicates to the Positioning PC that the Receivers will have made their measurements, and that the Positioning PC can now use the "Outgoing Data" bus to poll those Receivers to determine the results.
  • the Positioning PC can also retrieve the time at which the Receivers made their measurements by recovering the time held in the Time Store 218. It can also retrieve the latest measurement of the temperature in the room measured by a temperature sensor 222, the output of which is continually digitised by ADC 224 and stored in memory 226 for retrieval for example when the Receivers are reset.
  • the Positioning PC can also send commands to the ultrasound Receivers through the "Outgoing Data" bus to change the peak detection algorithm or thresholds used by the ultrasound Receivers.
  • the Matrix Manager When the Positioning PC asserts the "PC Ready” status line to indicate that it has performed all necessary actions associated with the current measurements, the Matrix Manager unasserts the "Result Ready” status line and prepares itself for the next clock pulse.
  • Data from the radio link (if utilised) between transceiver 208 and the mobile transponders is received via the upstream Network Interface 228 and transferred when instructed to a Data Path Selector switch 230 ( Figure 20) together with the digital temperature value from 226.
  • the global clock synchronization network signals pass unchanged through each Matrix Manager in turn.
  • the Receiver shown in Figure 22 detects ultrasonic signals from the transducer on the Mobile Transponders, and converts them to electric signals and processes those signals to determine the time at which the received acoustic signal peaked for the first time.
  • Receivers are connected in a serial daisy-chain to a Matrix Manager by two networks - an upstream network, 232 which carries information to the Matrix Manager, and a downstream network 234 which carries information from the Matrix Manager.
  • Each Receiver has an address which is unique amongst those connected to the same Matrix Manager, allowing it to be polled by the Positioning PC also connected to that Matrix Manager. The address may be coded for example by setting switches 235 on the PCBs of the Receivers.
  • a Receiver When a Receiver detects a "Reset” signal condition on the downstream network 234, it resets an on-board counter 236 and peak detection circuit 238. For the next 20ms, the counter is updated at a frequency of 20kHz, and the peak detection circuit monitors a signal from a 40kHz ultrasonic transducer which has been amplified in 242, rectified in 244, smoothed in 246 and digitized in 248.
  • the value 0 is formed in the counter.
  • the Receiver may be polled by the Positioning PC via the Matrix Manager and the downstream network 234. If an address comparator 250 in the Receiver links to the switch coded address 235 detects that the Receiver is being polled, the stored value in the counter is sent back to the Positioning PC via the upstream network 232 and Matrix Manager, together with error-checking information. Incoming information from other Receivers on the upstream network is blocked during this period.
  • Additional lines on the downstream network 234 can be used by the Positioning PC to change the peak detection algorithm used by the Receiver. Two algorithms may be used:
  • the threshold source may be a bank of switches 252 on the Receiver PCB, or a Threshold Memory 254.
  • the threshold source may, again, be changed by the Positioning PC by using lines on the downstream network.
  • the Positioning PC sets the poll address on the downstream network to the new value, and then asserts further lines such that each of the Receivers load the poll address value into a Temporary Threshold Memory 256.
  • the Positioning PC sets the poll address on the downstream network to the address of the Receiver whose threshold must be altered, and asserts further downstream network lines to transfer the value from the Temporary Threshold Memory 252 into the Threshold Memory 254 of the appropriate Receiver.
  • the Mobile Transponder shown in Figure 23 can be attached to objects, and generates ultrasonic signals 258 by which its position and possibly orientation can be determined.
  • Incoming radio messages from a Zone Manager are picked up by a 418MHz FM Radio Transceiver 260 and decoded by a Message Decoder 262.
  • the Message Decoder also uses error-checking information in the incoming messages to determine if bit errors on the radio link have occurred.
  • the Power-Saving Supervisory Circuit 264 switches off the receive side of the Radio Transceiver 160.
  • a Message Generator 266 allows the Mobile Transponder to contact the Zone Manager through the transmit side of the Radio Transceiver 260.
  • the Message Generator is used by a Registration Controller 268, which handles attempts to make the Zone Manager aware of the presence of the Mobile Transponder, and is also activated when a user presses one of two buttons 270, 272 on the Transponder" (if fitted).
  • the Message Decoder compares the transmitter address contained in the incoming message with that stored in ROM 274. If the addresses match, then:
  • the Registration Controller 282 is informed that the Zone Manager is now aware of this Mobile Transponder, and that no more registration attempts are needed.
  • the Mobile Transponder may attempt to send a data packet back to the Zone Manager through the transmit side of the 418MHz radio transceiver 260. This behaviour may be caused by a number of events:
  • a message generator waits a 25 ⁇ s turnaround time before switching on the transmit side of the Radio Transceiver 260, and sending (at 40kbps) a 168-bit preamble followed by a Manchester-encoded version of the packet whose format is shown in Table (B).
  • a Cyclic Redundancy Check code may be included in the packet to detect link errors or collisions with transmissions from other Mobile Transmitters.
  • a standard CRC-8 algorithm is used to generate the CRC.
  • the Message Generator After transmission of the preamble and packet, the Message Generator switches off the transmit side of the Radio Transceiver 260.
  • the Power-Saving Supervisory Circuit 264 is used to control other parts of the Mobile Transmitter in order to save power.
  • the Power-Saving Supervisory Circuit 264 decrements this counter once every 40ms, and only activates the receive circuitry of the Mobile Transmitter 260 once every eight timeslots (so that the wake bit periodically may be checked) .
  • the Power-Saving Supervisory Circuit 264 also controls an 8MHz clock 265 which is used by the Message Decoder 262 and Message Generator 266.
  • the Power-Saving Supervisory Circuit 264 sets sleep counter 286 to zero. This action ensures that the transmitter will check each incoming message until it is instructed that it no longer needs to do so.
  • the Mobile Transponder will enter a "Searching" mode. In this mode, the low-power supervisory circuit switches on the receive side of the 418MHz Radio Transceiver 260 approximately once every 80s, for a period of just over one second, and the Registration Controller 282 is informed that it should attempt to register with the Zone Manager.
  • the "Searching" mode is also the default state of the Mobile Transponder when it is switched on for the first time.
  • a 200MHz Pencium-pro IBM compatible PC with a 48 line parallel digital IO card may be used and the same hardware is suitable for all PCs shown.
  • each Matrix Manager Associated with each Matrix Manager is a Positioning PC 154, 168, 184 which computes the compositions of Mobile Transmitters from the time-of-flight values determined by Receivers 160, 1672 etc (whose surveyed positions are stored in memory by the Positioning PC). It continuously polls the Matrix Manager to determine whether the Receivers have been triggered and have results which should be processed. When the "Results Ready" status line is asserted by the Matrix Manager, the Positioning PC (via the Matrix Manager) polls each of the n Receivers connected to the Matrix Manager, retrieves a data value from each (along with error checking information), and unasserts the "PC Ready" status line.
  • the Positioning PC interrogates the Matrix Manager such as 166, 182 and determines the current temperature of the room, t (measured in °C). It is then possible to calculate the speed of sound in the room, c , from Equation (14).
  • Equation 15 If a Mobile Transponder is at the coordinates (u,v,w) and the distance from it to a Receiver at the coordinate (x,y,0) is l , are that all Receivers lie in the plane of the ceiling. It can be shown that l 2 is given by Equation 15.
  • Equation 1 can be regarded as a nonlinear model, see Myers, R. Classical and Modern Regression with Applications, PWS-KENT, 1990, and can use nonlinear regression to fit the values of l,x and y for several Receivers to this model. This gives estimates û, v and w and 2 . This allows the determination of a best least-squares estimate for the Mobile Transponder's position as the coordinate (û, v and,- ⁇ w and 2 ), taking the negative square-root of w and 2 to fix the transponder below the ceiling. A shadow solution ((û, v and,- ⁇ w and) corresponds to an impossible transmitter position above the ceiling.
  • the non-linear model has three degrees of freedom, and knowledge of at least three transponder-receiver distances is therefore required to calculate the Mobile Transponder's position. Furthermore, the model cannot be fitted to the data if all Receivers that detected a signal are collinear.
  • the first signal peak detected by a Receiver will be due to a pulse travelling along a direct line from the transponder. This pulse will arrive before any reflected pulses, which must travel along longer paths. The distance thus measured by the system will be that of a straight line joining transponder and receiver. Occasionally, however, the direct path may be blocked, and the first received signal peak will be due to a reflected pulse. In this case, the measured transponder-receiver distance will be greater than the true distance, leading to an inaccurate estimate of the transponder's position.
  • Two techniques have been developed for identifying and eliminating inaccurate distance measurements. First the difference of two transponder-receiver distances cannot be greater than the distance between the Receivers. If, by comparing pairs of measurements, two Receivers are found whose results do not satisfy this test, it can be seated that the larger of the two distances must be a measurement along a reflected path (remembering that reflections can only increase the measured distance), and can discard that result from the data set.
  • the statistical test is repeated until the variance of the remaining measurements fall below an acceptable threshold (suggesting that all outlying data points have been eliminated), or only three measurements remain. A final calculation of the transmitter's position is then made using those data values.
  • the Positioning PC then retrieves (from the Matrix Manager) the time at which the measurements used in the position calculation were made. Finally, it sends an event of the form (x, y, z, ⁇ , time) to the Area Manager across a CORBA interface, indicating the calculated position (x,y,z), orientation ( ⁇ ) and time of measurement, and informs the Matrix Manager that it is ready for the next set of readings (by asserting the "PC ready" status line).
  • Positioning PC (168, 184) can send commands to individual Receivers (via the Matrix Manager) to change the peak detection algorithm they use, or to change the threshold they store in memory, or to change the source of the threshold that the peak detection algorithm uses (either on-board switches, or memory).
  • data from the Scheduling and Positioning PC's is transmitted to the Area Manager 186 which comprises inter alia a data processor (such as a PC).
  • This gathers events of the form (identifier, time) from the Zone Manager, and events of the form (x,y, z, ⁇ , time) from each Matrix Manager.
  • An associative memory in the Area Manager links events using the time parameter, and generates a stream of events of the form (identifier, x,y,z, ⁇ ,time).
  • these events contain identification, location, orientation and time information, and therefore allow the position and orientation (at a particular time) of a transponder to be determined.
  • This event stream (shown at 288 in Figure 1) may be passed on to users and client applications.
  • Power saving can be achieved in the transponders by switching the receiver into a quiescent or OFF mode during the time intervals between addressing, and if the frequency at which a particular transponder unit is to be addressed is known this can be encoded into the radio message so that after decoding the message the receiver section can be turned off for that period of time.
  • control signals may be encoded into the radio addressing signals transmitted to the transponder units so as for example to control a display or robotic device, associated with the transponder unit.
  • Electrical signals indicative of the positions of a plurality of transmitters located at selected, strategic points on an object may be derived and stored and processed, for example by comparison with stored electrical signal data or processed by means of an algorithm, to produce a decision signal indicative of the shape of the object. This may enable a new object to be identified by reference to its shape.
  • Electrical signals indicative of the position and/or orientation of an object whose position and orientation (relative to the area) have been determined by position determining systems may be employed to control the display of a graphical representation of the object on a TV or computer monitor, together with graphical representations of other objects also identified by position (and orientation if measured).

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Burglar Alarm Systems (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Claims (15)

  1. System zum Bestimmen der Position eines jeden einer Vielzahl von markierten Objekten in einer speziellen, zu bestimmenden Umgebung durch Feststellen der Übergangszeit von langsam fortschreitender Energie, die von einem Sender auf jedem markierten Objekt an eine Vielzahl von Empfängern übertragen wird, die an fest vorgegebenen Stellen in oder um die bestimmte Umgebung positioniert sind, und durch Berechnen des tatsächlichen Abstands des Senders von den Empfängern hieraus, wobei die Übertragung der langsam fortschreitenden Energie durch einen Burst von mit hoher Geschwindigkeit fortschreitender Energie aus einem Haupt-Sender eingeleitet wird, der so positioniert ist, dass er übertragene Bursts solcher Energie hoher Geschwindigkeit in die Umgebung einführt, wobei der Sender auf dem Gegenstand durch einen Empfänger gesteuert wird, der auf einen entsprechend codierten Burst solcher Energie hoher Geschwindigkeit anspricht, wobei jeder Burst so codiert ist, dass er nur auf einen der auf dem Objekt befestigten Empfänger anspricht (jede Sender/Empfänger-Kombination wird als Transponder bezeichnet), um dadurch einen Burst von mit niedriger Geschwindigkeit fortschreitender Energie daraus herzuleiten, wobei die Lage des den Burst zur Entstehung bringenden Transponders aus der Codierung der Übertragung, die ihn triggert, identifizierbar ist und der Burst gerade eine ausreichende Zeitdauer wirksam ist, um ein Ansprechen an den Transponder-Empfängern zu erzielen, dadurch gekennzeichnet, dass zur Anpassung des Systems an unterschiedliche Service-Anforderungen unter Berücksichtigung einer unterschiedlichen Anzahl von Transpondern ein Koordinations-Steuersystem vorgesehen ist, das die Reihenfolge bestimmt, in der die auf dem Objekt befestigten Transponder-Sender durch die codierten Übertragungen von dem Haupt-Sender in Abhängigkeit von aktualisierbaren Informationen getriggert werden, die sich auf die Service-Anforderungen des Senders und/odervon Transpondern und/oder von Objekten beziehen.
  2. System nach Anspruch 1, bei dem die Codierung der mit hoher Geschwindigkeit erfolgenden Energie-Übertragung eine Vielzahl von unterschiedlichen, mit geringer Geschwindigkeit fortschreitenden Signalimpuls-Transponder/Sendern, die alle in der speziellen Umgebung angeordnet sind, in die Lage versetzt, dass sie der Reihe nach getriggert werden, damit während einer Folge von Zeitfenstern Positionsdaten, die sich auf jeden der mit geringer Geschwindigkeit fortschreitenden Signalimpuls-Transponder/Sender beziehen, in der Umgebung erhalten werden können, wobei die Daten in jedem Fenster sich speziell auf nur einen der auf dem Objekt befestigten Impuls-Transponder/Sender bezieht.
  3. System nach Anspruch 1 oder 2, mit mindestens drei feststehenden, nicht kolliniaren, verteilten, sich mit langsamer Geschwindigkeit ausbreitenden, auf Signale ansprechenden Empfängern, mindestens einem Transponder zum Übertragen von Signalimpulsen geringer Geschwindigkeit, der auf dem Objekt befestigt ist, mit einer Vorrichtung zum Erzeugen und Übertragen von Hochgeschwindigkeits-Signalimpulsen zum Synchronisieren einer mit geringer Geschwindigkeit arbeitenden Signalimpuls-Übertragung aus dem Transponder mit Beginn einer für einen Empfang empfindlichen Periode an einem Empfänger, und mit einer Vorrichtung zur Berechnung von Signalimpuls-Empfangszeiten und Korrelations-Unterschieden zur Bestimmung der gewünschten Informationen über die Position des Objektes.
  4. System nach Anspruch 3, bei dem das Koordinaten-Steuersystem eine Vorrichtung aufweist, um die auf dem Objekt befestigten Transponder zu adressieren, indem Adresseninformationen an sie als Teil eines regulären Zeit-Synchronisierungs-Signals gesendet werden.
  5. System nach einem der Ansprüche 1 - 4, bei dem das Koordinaten-Steuersystem so ausgelegt ist, dass es die Rangfolge bestimmt, in der die mit dem Objekt befestigten Transponder durch die Übertragungen aus dem Haupt-Sender zusammen mit einer Speichervorrichtung zur Speicherung relevanter Informationen über die unterschiedlichen Transponder/Sender durch Bezugnahme auf ihre eindeutige Adresse, durch die die Rangfolge bestimmt werden kann, adressiert und getriggert werden sollen.
  6. System nach Anspruch 5, bei dem die Speichervorrichtung des Koordinaten-Steuersystems eine eindeutige Adresse für jeden der Transponder/Sender speichert und das Steuersystem so programmiert ist, dass die Übertragungen, die die Adressen-Informationen benutzen, codiert werden, so dass nur die Transponder/Sender individuell adressiert werden.
  7. System nach Anspruch 6, bei dem zusätzlich zu der eindeutigen Adresse für jeden Transponder mindestens ein zusätzlicher Informationsausdruck (gewichtete Hierarchie-Information für Management-Positionierung- oder "WHISP") in solcher Weise gespeichert wird, dass er jeder eindeutigen Adresse zugeordnet werden kann, und das Steuersystem so programmiert ist, dass aus den Adressen die Adresse des Transponders ausgewählt wird, die der abgefragten unter Verwendung der WHISP-Werte am nächsten liegt, damit die Rangordnung der Adressierung bestimmt wird.
  8. System nach Anspruch 7, bei dem eine WHISP für jede eindeutige Adresse gespeichert wird und die WHISP zur Einstellung der nachfolgenden Adressierung der Transponder geändert wird.
  9. System nach Anspruch 7 oder 8, bei dem jede WHISP zwei Informationsausdrücke aufweist, nämlich einerseits die Zeitdauer, seit der der Transponder zuletzt adressiert worden ist, und ferner eine Rate der Abfragungszahl, die durch das System für diesen Transponder/Sender erreicht werden soll.
  10. System nach Anspruch 9, bei dem die Länge der Zeitdauer seit der letzten Adressierung des Transponders kontinuierlich durch Taktgeber-Informationen fortgeschaltet wird.
  11. System nach einem der Ansprüche 1 - 10, bei dem Änderungen an den WHISP-Daten als Ergebnis einer verstrichenen Zeit, der Ankunft einer bestimmten Zeit oder eines Datums durch Wechselwirkung mit einer auf einem Rechner laufenden Anwendung auftreten, die Teil des die Position bestimmenden Systems oder des Koordinaten-Steuersystems oder eines ganz anderen Rechners sein kann, oder durch das Einführen von Daten z.B. durch einen Operator, um anzuzeigen, dass das System seine Zeitplan-Funktion zur Bestimmung der Position des Transponder/Senders beenden und eine bestimmte Transponder/Sender-Adresse suchen soll.
  12. System nach einem der Ansprüche 7-11, das so programmiert ist, dass es einen dritten Datenausdruck innerhalb einer WHISP verwendet, und eine logische Schaltvorrichtung vorgesehen ist, um die Verfolgung einer Adresse eines ersten Objektes zu erhöhen, wenn ein zweites Objekt, das einen solchen dritten Informationsausdruck als Teil seiner WHISP gespeichert hält, von der Positionsbestimmung des zweiten Objektes wahrgenommen wird, dass es sich nahe an das erste Objekt bewegt hat.
  13. System nach einem der Ansprüche 1 - 12, bei dem ein Satz von Ultraschall-Empfängern an bekannten Positionen auf einer Decke in einem Raum angeordnet sind, um Ultraschall-Signale aus einem Impuls-Übertrager, der mit einem Objekt im Raum verbunden ist, zu detektieren, und durch Bestimmen die Zeitdauer der Bewegung dieser Signale von dem Transponder zu den Ultraschall-Empfängern in drei Dimensionen die Position dieses Objektes in dem Raum bestimmt wird, wobei das Koordinaten-Steuersystem mehr als einen Transponder adressiert, vorausgesetzt, dass jeder eine eindeutige Adresse besitzt, damit sie durch serienweises Abrufen der Transponder in Abhängigkeit von Steuersignalen aus dem Steuersystem getrennt getriggert werden können.
  14. System nach einem der Ansprüche 1 - 13, bei dem eine Zweirichtungs-Kopplung zwischen dem Koordinaten-Steuersystem und jedem Transponder vorgesehen ist, indem ein zweiter Sender jedem Transponder und ein kompatibler Empfänger dem Koordinations-Steuersystem hinzugefügt wird, wobei solche Transponder als Zweirichtungs-Transponder bezeichnet werden, und wobei letztere ermöglichen, Daten in das Koordinations-Steuersystem zu übertragen.
  15. System nach einem der vorausgehenden Ansprüche, bei dem jeder Transponder ferner Eingabe- und/oder Ausgabe-Möglichkeiten aufweist.
EP97947785A 1996-12-04 1997-12-04 Erkennungssystem zur bestimmung der position und anderer objektbezogener information Expired - Lifetime EP0943102B1 (de)

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GBGB9625208.5A GB9625208D0 (en) 1996-12-04 1996-12-04 Detection system for determining information about objects
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PCT/GB1997/003359 WO1998028634A2 (en) 1996-12-04 1997-12-04 Detection system for determining positional and other information about objects

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DE10339581A1 (de) * 2003-08-28 2005-03-24 Teltix Gmbh Verfahren und Vorrichtung zur Ortung einer elektromagnetische Strahlung emitierenden Quelle
DE102005056231A1 (de) * 2005-11-25 2007-06-06 Bayerische Motoren Werke Ag Verfahren und Vorrichtung zur Funktionskontrolle eines elektrisch angetriebenen Fahrzeugteils

Also Published As

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WO1998028634A3 (en) 1998-08-27
GB2320089A (en) 1998-06-10
US6493649B1 (en) 2002-12-10
GB2320089B (en) 2001-06-20
GB9725760D0 (en) 1998-02-04
DE69711682D1 (de) 2002-05-08
EP0943102A1 (de) 1999-09-22
ATE215701T1 (de) 2002-04-15
GB9625208D0 (en) 1997-01-22
WO1998028634A2 (en) 1998-07-02
DE69711682T2 (de) 2002-11-14

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